1. Field of the Invention
The present invention relates to a vapor processing apparatus.
2. Discussion of the Background
In a fuel tank retaining fuel to be supplied to an engine of a vehicle, part of the fuel evaporates into vapor. To prevent a large quantity of such vapor from being released into the atmosphere, vehicles including engines have vapor processing apparatuses.
For example, if the inner pressure of the fuel tank is high when opening the filler pipe opening, a large amount of vapor will be discharged from the filler pipe opening into the atmosphere, causing air pollution. Therefore, when the filler pipe opening is opened, the vapor generated in the fuel tank is collected by a vapor processing apparatus to prevent the vapor from being discharged into the atmosphere.
The vapor generated in the fuel tank can be supplied to the engine, where it is combusted. However, for a vehicle that uses an engine and a driving motor (i.e., a hybrid vehicle), the engine is driven for a reduced amount of, and thus the vapor may not be fully combusted in the engine. Therefore, for hybrid vehicles in particular, since vapor tends to accumulate in the fuel tank, vapor discharge from the filler pipe opening must be reliably prevented.
For example, Japanese Unexamined Patent Application Publication No. 2001-123891 discloses a vapor-discharge prevention apparatus (vapor processing apparatus) configured to prevent vapor discharge into the atmosphere by maintaining negative pressure in the fuel tank.
With the vapor-discharge prevention apparatus in Japanese Unexamined Patent Application Publication No. 2001-123891, a control valve is controlled in accordance with the pressure inside the fuel tank and the atmospheric pressure to maintain negative pressure in the fuel tank.
The vapor-discharge prevention apparatus that is disclosed in Japanese Unexamined Patent Application Publication No. 2001-123891 detects the absolute pressure of the fuel tank inner pressure with a tank-inner-pressure sensor and detects the absolute pressure of the atmosphere with an atmospheric-pressure sensor. Then, gauge pressure inside the fuel tank, which is based on the atmospheric pressure, is calculated from the atmospheric pressure (absolute pressure) detected by the atmospheric-pressure sensor and the inner pressure (absolute pressure) of the fuel tank detected by the tank-inner-pressure sensor, and a tank-inner-pressure control valve, which controls the inner pressure of the fuel tank, is controlled in accordance with the calculated fuel tank gauge pressure.